A known intake manifold is disclosed in JP2010-65575A (hereinafter referred to as Patent reference 1). The known intake manifold, for example, disclosed in Patent reference 1 is provided with plural intake pipes corresponding to each air cylinder in an internal combustion engine and a blow-by gas distribution part connected to the intake pipes. At least one of inlet paths communicating the blow-by gas distribution part with intake pipes is positioned at a bottom portion of the blow-by gas distribution part while at least one of the inlet paths is positioned at an upper portion than the bottom portion of the blow-by gas distribution part (see, for example, Patent reference 1).
A known intake manifold, for example, disclosed in JP2010-84640A (hereinafter referred to as Patent reference 2) is provided with plural intake pipes corresponding to each air cylinder in an internal combustion engine and a blow-by gas distribution part connected to the intake pipes. The known intake manifold includes inlet paths communicating the blow-by gas distribution part with intake pipes and a lower surface of the inlet paths declines from the blow-by gas distribution part to the intake pipes while a lowermost end surface of the blow-by gas distribution part is positioned higher than a lowermost end surface of the inlet paths (see, for example, Patent reference 2)
According to the intake manifold disclosed in Reference 1, an inflow of liquid including water and oil generated from blow-by gas from the inlet paths positioned at the bottom portion of the blow-by gas distribution part to a part of the intake pipes may cause engine misfire and torque fluctuation in which output torque in each air cylinder of an engine differs from one another.
According to the intake manifold disclosed in Reference 2, an inflow of liquid including water and oil generated from blow-by gas from the inlet paths positioned at the blow-by gas distribution part to a part of the intake pipes may cause engine misfire and torque fluctuation.
A need thus exists for an intake manifold which is not susceptible to the drawback mentioned above.